Order ANOMOPODA G.O. Sars, 1865

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Order ANOMOPODA G.O. Sars, 1865

Anomopoda Sars, G.O. 1865. Norges ferskvandskrebsdyr. Første Afsnit. Branchiopoda. 1. Cladocera Ctenopoda (Fam. Sididae & Holopedidae) [Norway's freshwater crustaceans. First part. Branchiopoda. 1. Cladocera Ctenopoda (Fam. Sididae & Holopedidae)]. Christiania : Brøgger & Christie's Bogtrykker pp. i-viii, 1-71, pls 1-4. [https://wellcomecollection.org/works/s4qp43x7] [vii].

Introduction

The Anomopoda, contains most of the species within the Branchiopoda. Anomopodans are found in a very broad variety of biotopes, mostly in fresh water (both permanent and ephemeral) but few species are restricted to saline water (Moina salina, Alona salina), where they are planktonic, (hypo)neustonic, littoral, or benthic. Several bosminids have become adapted to a relatively high salinity, like in the Baltic Sea. Other species are ectoparasitic, stygobitic, or semiterrestrial. Anomopods occur world-wide. The order is monophyletic, supported by a suite of apomorphies – the appearance of a ‘unique ejector hook of the first trunk limb, reduction of serial similarity of trunk limbs, by the appearance of an ephippium, antennae with two proximal setae and vacuolar maturation of spermatids (Olesen, 1998). Dumont & Silva-Briano (1998) proposed a new order Radopoda within this group but it has not been generally accepted except by Schram & Koeneman (2021).

Diagnosis

Body short, more or less laterally compressed, indistinctly segmented and ending in a postabdomen with an apical pair of claws (rarely absent), which sometimes articulates to the trunk. Carapace not calcified, bivalved, without hinge, enclosing only the trunk and appendages, often with modifications (e.g., along the ventral rim; sometimes honeycombed; rarely with growth lines). Head short. Head-shield usually well developed. Labrum fleshy. Eyes single, internal, always fused in adults, from small to big, usually w1th few lenses, secondarily absent in Monospilus, in the semi-terrestrial genera Bryospilus and Nicsmirnovius, and in subterranean species of Alona. Ocellus present except in blind cave species. Antennules tubular, of 1 or 2 segments, more or less large, occasionally reduced to small papillae (in females), and usually modified for clasping, often longer and with grappling spine in males. Antennae biramous, natatory, used in some species for crawling on the bottom or on plants; exopod of 3 or 4 segments and endopod of 3 segments, armed with up to 9 long natatory setae and spines; sometimes a short termmal spme on both rami. Mandibles of the grinding type. Maxillules with few spines (maximum 4). Maxillae reduced to a mound or absent. Five or six pairs of trunk limbs of variable shape and size according to function, but none in postgenital position. Exopodites and epipodites (sometimes pre-epipodites) present. First and sixth pair (if present) non-filtratory. First pair frequently used in locomotion. Others modified for grasping, scraping and guiding particles, and for sweeping or filtration according to speciies and position in the row of limbs. No metachronal beating rhythm. First trunk limb of males with apical clasping hook, and usually with long additional seta or extra spine. Food groove deep and narrow. Alimentary canal with various modifications: straight or convoluted, with or without a pair of anterior caeca, with or without posterior diverticulum, and with or without tubular and glandular organ. Ovaries paired; ovarian cells originate posteriorly. No penis, except in Leydigia, where the sperm ducts open in a "penis" placed between the claws of the postabdomen. Vasa deferentia open at distal end of a postabdomen which is more or less modified for copulation (not in Eurycercus). Resting eggs produced during a short period of the cycle, enclosed in a case made from the whole or part of the carapace. The number of eggs variable, 1–15. Resting eggs encased in a simple protective case (Macrothricidae) or, in well determined number (usually one or two) a in a specialise ephippium (Daphniidae). Parthenogenetic eggs large, laid in a dorsal brood pouch where they develop to small replicas of adults. A nährboden is only found in the Moininae. Parthenogenesis and gamogenes is alternate, but gamogenesis maybe suppressed. Some arctic and some tropical taxa are suspected of obIigate parthenogenetic reproduction (especially some arctic Daphnia). Gamogenetic periods short. No larval stages: sexual young are also replicas of adults. Length from 0.22 mm to c. 6 mn in females, 0.16 mm to 2.2 mm in males (smallest species Alonella nana, largest Daphnia magna).